Page 27 - FAO-IPCC Expert meeting on climate change

Direct climate impacts on land-ecosystems and food provision
5
There is increasing agreement among scientists that climate change constitutes a threat to pollinators and scientific evidence to support this is slowly amassing.6 The threat to wild pollinators for crop production is, indeed, serious. Many species are responding to climate change by shifting upwards and further north in terms of altitude and latitude, respectively.
Studies in Europe demonstrate that by 2100 pollinators are expected to transfer to new areas and that their distribution will diverge from those where fruits and orchard trees are optimally grown. This trend may result in smaller pollinator populations and, hence, smaller crop yields. The migration of pollinators, such as the hummingbird, also is changing as they reportedly migrate sooner than they did heretofore.
Climate change is also causing a timing mismatch between pollinators and crops with evidence that crop flowering and the activities of pollinators occur at different times as a result. For example, having spent the winter underground, bumble bees may emerge either earlier or later in spring so they are unable to pollinate wild flowers when they are in bloom. Studies in the United States reveal a changing phonology of apple tree flowering. In the past, the emergence of bumble bees to pollinate the flowers on apple trees coincided pretty well. But scientists are now predicting an earlier blooming of this flower, a change that will affect pollinators, creating a time gap in pollination and therefore negatively affecting yields. Another problem with flowering apple trees resulting from climate change is earlier flowering, making them susceptible to frost and resulting in a significant crop loss.
Evidence on crop-pollinator dynamics under climate change, so far, is relatively scant. Some studies have alluded to
a crop-pollinator mismatch, although most do not. Ecologists, nevertheless, now confirm that there is evidence of a change, for example the fact that bumble bees are evolving in terms of peak numbers and that spatial and temporal developments are occurring and affecting crop pollination. Much less, however, is known about the physiological effect on partners. Crops and pollinators that are close to the thermal limit are seen to perform worse as climate temperatures rise. Pollinators are becoming smaller, live shorter periods and there are fewer plants and blossoms. More research is clearly essential to improve the understanding of such climate-induced physiological changes and the growing threats of reduced pollination services to food production.
Finally, an important gap in the literature is the identification and understanding of cumulative and combined impacts of climate change on species, habitats and communities. While pollinators become extinct, increases in temperature and a shift in moisture regimes are likely to increase the proliferation of various pests and diseases and induce changes in crop pathogens, which further threaten crop-pollinator dynamics.
There is also evidence that chemical use on farms is a major threat and may exacerbate the loss of pollinators even more than climate
6
change.
FAO-IPCC Expert meeting on climate change, land use and food security